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On the Complexity of Reasoning in Kleene Algebra
 Information and Computation
, 1997
"... We study the complexity of reasoning in Kleene algebra and *continuous Kleene algebra in the presence of extra equational assumptions E; that is, the complexity of deciding the validity of universal Horn formulas E ! s = t, where E is a finite set of equations. We obtain various levels of complexi ..."
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Cited by 10 (4 self)
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We study the complexity of reasoning in Kleene algebra and *continuous Kleene algebra in the presence of extra equational assumptions E; that is, the complexity of deciding the validity of universal Horn formulas E ! s = t, where E is a finite set of equations. We obtain various levels of complexity based on the form of the assumptions E. Our main results are: for * continuous Kleene algebra, ffl if E contains only commutativity assumptions pq = qp, the problem is \Pi 0 1 complete; ffl if E contains only monoid equations, the problem is \Pi 0 2 complete; ffl for arbitrary equations E, the problem is \Pi 1 1  complete. The last problem is the universal Horn theory of the *continuous Kleene algebras. This resolves an open question of Kozen (1994). 1 Introduction Kleene algebra (KA) is fundamental and ubiquitous in computer science. Since its invention by Kleene in 1956, it has arisen in various forms in program logic and semantics [17, 28], relational algebra [27, 32], aut...
Overview of Complexity and Decidability Results for Three Classes of Elementary Nonlinear Systems
"... It has become increasingly apparent this last decade that many problems in systems and control are NPhard and, in some cases, undecidable. The inherent complexity of some of the most elementary problems in systems and control points to the necessity of using alternative approximate techniques to ..."
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Cited by 9 (7 self)
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It has become increasingly apparent this last decade that many problems in systems and control are NPhard and, in some cases, undecidable. The inherent complexity of some of the most elementary problems in systems and control points to the necessity of using alternative approximate techniques to deal with problems that are unsolvable or intractable when exact solutions are sought. We survey
Subrecursion as Basis for a Feasible Programming Language
 Proceedings of CSL'94, number 933 in LNCS
, 1994
"... We are motivated by finding a good basis for the semantics of programming languages and investigate small classes in subrecursive hierarchies of functions. We do this with the help of pairing functions because in this way we can explore the amazing coding powers of Sexpressions of LISP within t ..."
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Cited by 9 (8 self)
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We are motivated by finding a good basis for the semantics of programming languages and investigate small classes in subrecursive hierarchies of functions. We do this with the help of pairing functions because in this way we can explore the amazing coding powers of Sexpressions of LISP within the domain of natural numbers. In the process of doing this we introduce a missing stage in Grzegorczykbased hierarchies which solves the longstanding open problem of what is the precise relation between the small recursive classes and those of complexity theory. 1 Introduction We investigate subrecursive hierarchies based on pairing functions and solve a longstanding open problem in small recursive classes of what is the relationship between these and computational complexity classes (see [11]). The problem is solved by discovering that there is a missing stage in Grzegorczykbased hierarchies [7, 11]. The motivation for this research comes from our search for a good programming langu...
A Survey on Embedding Programming Logics in a Theorem Prover
 Institute of Information and Computing Sciences Utrecht University
, 2002
"... Theorem provers were also called 'proof checkers' because that is what they were in the beginning. They have grown powerful, however, capable in many cases to automatically produce complicated proofs. In particular, higher order logic based theorem provers such as HOL and PVS became popula ..."
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Cited by 8 (2 self)
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Theorem provers were also called 'proof checkers' because that is what they were in the beginning. They have grown powerful, however, capable in many cases to automatically produce complicated proofs. In particular, higher order logic based theorem provers such as HOL and PVS became popular because the logic is well known and very expressive. They are generally considered to be potential platforms to embed a programming logic for the purpose of formal verification. In this paper we investigate a number of most commonly used methods of embedding programming logics in such theorem provers and expose problems we discover. We will also propose an alternative approach: hybrid embedding.
On the Simplicity and Speed of Programs for Computing Infinite Sets of Natural Numbers
 J. ASSOC. COMPUT. MACH
, 1969
"... It is suggested that there are infinite computable sets of natural numbers with the property that no infinite subset can be computed more simply or more quickly than the whole set. Attempts to establish this without restricting in any way the computer involved in the calculations are not entirely su ..."
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Cited by 8 (1 self)
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It is suggested that there are infinite computable sets of natural numbers with the property that no infinite subset can be computed more simply or more quickly than the whole set. Attempts to establish this without restricting in any way the computer involved in the calculations are not entirely successful. A hypothesis concerning the computer makes it possible to exhibit sets without simpler subsets. A second and analogous hypothesis then makes it possible to prove that these sets are also without subsets which can be computed more rapidly than the whole set. It is then demonstrated that there are computers which satisfy both hypotheses. The general theory is momentarily set aside and a particular Turing machine is studied. Lastly, it is shown that the second hypothesis is more restrictive then requiring the computer to be capable of calculating all infinite computable sets of natural numbers.
Communication, computability, and common interest games
 Games and Economic Behavior
, 1990
"... This paper provides a theory of equilibrium selection for oneshot twoplayer niteaction strategicform Common Interest games. A single round of costless unlimited preplay communication is allowed. Players are restricted to use strategies which are computable in the sense of Church's Thesis. ..."
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Cited by 7 (0 self)
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This paper provides a theory of equilibrium selection for oneshot twoplayer niteaction strategicform Common Interest games. A single round of costless unlimited preplay communication is allowed. Players are restricted to use strategies which are computable in the sense of Church's Thesis. The equilibrium notion used involves perturbations which are themselves computable. The only equilibrium payo vector which survives these strategic restrictions and the computable perturbations is the unique Paretoe cient one. JEL Classification: C72,C79.
The Interactive Nature of Computing: Refuting the Strong ChurchTuring Thesis
, 2007
"... The classical view of computing positions computation as a closedbox transformation of inputs (rational numbers or finite strings) to outputs. According to the interactive view of computing, computation is an ongoing interactive process rather than a functionbased transformation of an input to a ..."
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Cited by 6 (0 self)
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The classical view of computing positions computation as a closedbox transformation of inputs (rational numbers or finite strings) to outputs. According to the interactive view of computing, computation is an ongoing interactive process rather than a functionbased transformation of an input to an output. Specifically, communication with the outside world happens during the computation, not before or after it. This approach radically changes our understanding of what is computation and how it is modeled. The acceptance of interaction as a new paradigm is hindered by the Strong ChurchTuring Thesis (SCT), the widespread belief that Turing Machines (TMs) capture all computation, so models of computation more expressive than TMs are impossible. In this paper, we show that SCT reinterprets the original ChurchTuring Thesis (CTT) in a way that Turing never intended; its commonly assumed equivalence to the original is a myth. We identify and analyze the historical reasons for the widespread belief in SCT. Only by accepting that it is false can we begin to adopt interaction as an alternative paradigm of computation. We present Persistent Turing Machines (PTMs), that extend TMs to capture sequential interaction. PTMs allow us to formulate the Sequential Interaction Thesis, going beyond the expressiveness of TMs and of the CTT. The paradigm shift to interaction provides an alternative understanding of the nature of computing that better reflects the services provided by today’s computing technology.